1. Field of the Invention
This invention relates generally to reference voltage generator circuits and more particularly, it relates to an improved reference voltage generator circuit for use with an extremely low power supply which is compensated for temperature variations and is independent of changes in the supply voltage.
2. Description of the Prior Art
As is generally known, virtually all types of electronic circuits utilizing integrated circuits require reference voltages. It is typically desired that the reference voltage be constant under all operating conditions and have essentially no temperature drift or a defined temperature drift. One type of prior art reference voltage circuit that produces such a constant voltage is referred to as a "bandgap" reference voltage circuit. The reference voltage generated by such a bandgap circuit is temperature-independent of the circuit components used and corresponds to the bandgap of a semiconductor material. Frequently, the semiconductor material used is silicon and thus furnishes a temperature-independent reference voltage of approximately 1.205 volts. Further, this bandgap circuit relies upon the use of the base-to-emitter voltage V.sub.be (with a negative temperature coefficient) of a bipolar transistor as a reference which is compensated for through a voltage having a positive temperature coefficient that is added.
However, these existing prior art bandgap reference voltage circuits suffer from the principal disadvantage that they will not operate when the power supply voltage VCC is reduced down to an extremely low voltage such as 1 volt. In view of the trend for deep-submicron CMOS technology, lower and lower supply voltages are being used. Further, the regulated output voltage from the bandgap circuit has the added drawback of only being able to produce a reference voltage equal to about 1.205 volts or a multiple thereof.
Therefore, it would be desirable to provide a reference voltage generator circuit which is adapted for use with an extremely low power supply voltage. Further, it would be expedient that the reference voltage generator circuit produce a low output voltage which is temperature-compensated and is independent of variations in the power supply voltage.